In recent years, researches on low-temperature semiconductor fabrication processes have been earnestly conducted, because it is necessary to form semiconductor devices on an insulating substrate made of glass or the like or on an insulating coating formed on the semiconductor substrate and for other reasons. To fabricate these semiconductor devices, it has been necessary to thermally treat them. For example, in order to thermally crystallize a semiconductor coating which takes an amorphous state or a low crystallinity equivalent to the amorphous state, or to reduce unpaired electrons, or dangling bonds, in insulating films and semiconductor films, a thermal treatment performed at approximately 1000.degree. C. is needed.
However, where devices are formed on a glass substrate, it is necessary that the glass substrate withstand such high-temperature thermal treatment. Where semiconductor devices are formed on a semiconductor substrate, i.e., plural layers of semiconductor are formed, if the lower layer of devices has conductive interconnects of a low-melting metal, then it is not possible to perform a high-temperature treatment.
Accordingly, methods (including laser annealing) of creating a requisite local high-temperature state by laser irradiation in such a way that neither the substrate nor other conductive interconnects are damaged have attracted attention as ideal low-temperature processes. Especially, irradiation of short laser pulses less than 1 .mu.sec is an ideal method because other portions are hardly affected by conduction of heat. Among others, the use of an excimer laser emitting ultraviolet radiation has been considered to be most practical, because ultraviolet radiation is efficiently absorbed by many materials and because a large energy can be obtained.
However, severe laser processing conditions have heretofore existed. In consequence, laser processing techniques are far from stable techniques and do not provide sufficiently high reliability. Hence, it has generally been considered that laser processing techniques will never be put into practical use.